Luminescence of ZnMoO₄ Crystals Developed for the LUMINEU Double Beta Decay Experiment

Scintillation efficiency of ZnMoO4 crystals is one of the main characteristics for application in cryogenic double beta decay experiments. Luminescence of ZnMoO4 crystals developed from deeply purified molybdenum under X-ray irradiation of different doses was studied in the temperature interval from 1.4 K to 295 K. Emission spectra, dependence of luminescence intensity on dose and temperature, phosphorescence and thermally stimulated luminescence were investigated. Two emission bands were identified: recombination luminescence at ~ 600 nm and exciton luminescence at ~ 500 nm. We have found that concentration of shallow traps in the material is much greater than the concentration of deep traps. Furthermore only shallow traps absorb a small part of the luminescence and cause the low scintillation efficiency of the sample.